The present invention is directed to the use of waste water produced as a byproduct of an osmotic membrane application and the subsequent use of that water for cooling tower applications whereby the subsequent use of the water in such application is highly conserved and further operative to reduce scale and inhibit corrosion. As is known, reverse osmosis (RO) reject has been used as cooling tower makeup in conjunction with traditional scale and corrosion control treatment methods for cooling tower water, but to do so requires significant increased chemical treatment cost and increased cooling tower discharge of the dissolved mineral concentrates in the tower water to avoid scale and corrosion performance consequences. Thus, there was marginal value in operation of the RO system at increased operating efficiencies by increasing RO reject (reduced feed water recovery rates), as RO reject waste disposal and cost burdens were simply transferred to the cooling tower system water wastage disposal costs. Likewise, RO operators are likely to use the best quality feed water available to reduce RO reject waste volume and RO operating costs, which is usually our scarcer and more limited supply of city potable water and other broadly useful fresh water sources.
Increased RO reject wastage, particularly with use of softened RO feed water and thus soft RO reject, has also been applied for use as cooling tower makeup, but with only limited water consumption and discharge reduction benefits since the RO reject water and concentrated dissolved solids were simply being deferred to the cooling tower system for discharge from the cooling tower by blow down with use of traditional scale and corrosion index type chemistry treatments which rely on waste of a significant proportion of the tower water and dissolved solids content to avert scale and corrosion consequences. Thus, any increased RO efficiencies resulting from increasing reject flow is offset by additional costs for increased volume of RO pretreated quality feed water consumed and the deferred waste disposal costs for such combinations of RO reject use and traditional cooling tower water treatment (blow down wastage) required, which makes the practice economically and environmentally impractical and undesirable.
Forward osmosis (FO) processing has likewise recently been explored and applied to produce a source of or cooling tower makeup from brackish water sources in conjunction with use of specific manufactured chemicals introduced to the evaporative cooling water system to create a suitable osmotic or draw solution, along with use of traditional scale and corrosion control treatment methods in the cooling tower water or draw solution system. Such practices also require substantial evaporative system water discharge and/or osmotic agent recovery (removal) to avoid scale and corrosion performance consequences in the cooling system and FO process.
Review of referenced publications, studies and patents, however, disclose general deficiencies in FO processes relative to providing sufficient extraction/recovery efficiency of water to compete economically with traditional RO processes that have more highly developed membrane system designs suitable to provide the required water quality when using inferior water quality sources. The recognized disadvantages with RO processes are due primarily to the energy intensive pressure driven process and membrane fouling potentials, but these disadvantages are not outperformed economically by FO processes due to poor extraction efficiencies. The disclosed FO deficiencies are thus primarily related to cost and performance for providing suitable osmotic draw solutions, efficient osmotic extraction membrane designs, recovery of osmotic agent from the draw solution, draw solution heating, and associated further chemical treatment of the draw solution to avert scale, corrosion and biological maintenance and performance issues in the cooling tower system.
Thus, there is marginal value in the operation of the FO system as a water source for such application unless warranted by extreme scarcity of fresh water sources. The FO process would benefit from increased operating cost efficiencies by increasing FO extraction or recovery rates, reduced capital footprint costs, reduced waste production, and expansion of the range of inferior water sources that can be utilized to avert use of fresh water sources. To date, however, such commercially viable applications do not exist.
The following publications and patents identified below are believed to be pertinent as reference materials with respect to the subject matter of the present invention, all of which are expressly incorporated herein by reference.